This is the mechanism for the real original Wacker procedure, where lower alkenes are oxidised in an all AQUEOUS solution. This reaction is much slower that the one in alcohol.When the solvent is an alcohol and no water is present something else takes place:

The product for anhydrous conditions is R-C(-OR')2-CH3, the so called ketal. Semiketal would be R"-C(-OR')(OH)-CH3, a side product when sub-stoichometrical amounts of water are present.

Note the following similarity:H---O---HR'---O---HMeaning the reaction doesn't mind if it is done in H2O or ROH solvent, it just happens that the latter is much faster. In that 1969 ref they clearly found that increasing amounts of water slow down the reaction considerably.

So, the product of an all-ROH-no-H2O Wacker will be R2-C(O-R')2-CH3. This is quickly hydrolysed in acidic aqueous media. Since the Wacker mix is slightly acidic adding water alone would already work, but everybody uses diluted HCl for that step anyway so the hydrolysis to the ketone is very fast, forming two moles of the alcohol and one mole of the ketone.

I'm not doubting your results, but in my experience no water is needed in that reaction. It worked well without for me. The catalysts recycled well in the alcohol solvent, or with that little water that was preent due to CuCl2.2H2O usage.

The DMF wacker needs water because the DMF can't add across the double bond like water or alcohols can. Haven't thought about it yet but I think that benzoquinone reduction needs some water too, since DMF is dipolar-APROTIC. Besides nobody has posted a DMF Wacker with reduced water yet. Everybody just used the literature numbers for H2O/DMF 1/7 or whatever they are, nobody tried to reduce the water to the bare minimum yet. It might run much faster with reduced water content, or slow water addition during the reaction.

And at least in my corner of the world the tech grade MeOH and IPA I bought were close to reagent grade purity, but I used barreled stuff from a chem supplier (still cheapest grade available) not some OTC source. But I still doubt that they contain 1% water. Purity statements on the label are usually guaranteed minimum purities, don't take them too literally thinking when it says it's 99% the it must be exactly 99% pure. That purity also depends on how it was determined, GC for example can't detect H2O. When I buy tech grade MeOH there will be EtOH in it, along with formaldehyde, acetone, other alcohols etc, making up that missing 1%.

frost

the ketal will turn into ketone when the ketamine injects.....woah. when it hits the dh20/hcl solution ikt will hydrolyse into ketone within minutes. damn did somebody,antibody see that K TRAIN that just ran over mee.anyway, ab2 ketal is the post wacker ketone before the hcl addition. then and only then will the KETONE appear.digging deeper and deeper into that hole........guess who's off today!

scram

Yeah FIGHT, FIGHT! This is a interesting reaction. I've notice better yields with pressure either at 40-50psi or 75+. For some reason yields were always less between 50 to 75 psi. Frost that water in the al/hg comes from the nitro reaction because it produces water by itself.

Osmium

Define "most effective": fastest, cleanest or highest yielding? Or most cost-efficient? Or anything else?What kind of alkenes did he use? What chain lenght?I'm not familiar with that ref, BTW.

When doing a chemical reaction which is unwilling to proceed you usually have two options: you can either push it from the left side of the equation (for example by using an excess of one reactand) or you can pull it from the right side (e.g. by removing one of the products by distillation or extraction or chemical means). That's what that guy obviously did, extracting the alkene into the water layer and removing the product ketone after the reaction back into the organic layer where it will stay unchanged for the rest of the reaction. So he kept the alkene concentration pretty much constant in the water layer throughout the reaction (concentration is determined by solubility of the Pd--alkene complex), and drove the reaction to the right by completely removing the product from any further attack into the organic layer since it is pretty much insoluble in the water layer and won't form soluble complexes anymore. By using a biphasic system he still performed the reaction in the water phase, and used the organic phase as a reservoir for the reactand and the products. Of course that way the organic phase doesn't contribute to the reaction. The catalysts love water way better than the organic layer, so that's where they will be (I guess). And how did he achieve phase separation with the lower alcohols?Did that guy use some sort of PTC in that reaction too? If he did then things really get complicated, because there are many different reaction modes possible depending on a shitloads of factors and any comparison to our topic here becomes pure speculation.

Ketals are pretty efficient protective groups, but I don't know for sure just how good they are under oxidative conditions like the wacker.

That 1969 ref clearly says that the lower alcohols were the fastest solvents, with the highest reaction rates found.One of the original Wacker refs by Jira et. al. from the fifties even contains an example where they used safrole in the aqueous Wacker, yields were definitely worse than the ones you describe for the alcoholic Wacker.

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dunkel

Osmium, when you did the Wacker in the old days using MeOH as solvent, didn't you add some acidic water after the reaction was completed, then distill off the MeOH or EtOH? I think this added heat and time is necessary for effective conversion of the ketal to the ketone. In the US patent 4638094 for making phenylacetones when they perform the reaction in anhydrous conditions, at the end they add water and heat to convert the ketal to the ketone. Otherwise they add water to the reaction in the begining to end up with just ketone at the end without having to heat.

I'm not sure if just adding water at the end and immediately extracting (which most people are doing) will spontaneously convert the ketal into the ketone. The water that is already present during the course of the wacker reaction will convert some of the ketal into the 'tone. While the majority (if NO water is added) will be in the form of the ketal.

As far as quickness, since you are using alcohol as solvent and nucleophile, -0R addition (aka ketal formation), will be the fastest compared to the water.

Just my $0.02. Only one way to find out...

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Antibody2

Precurser2112. Vac filtering this rxn sux. But is greatly facilitated by the use of 2cm of silica sand in buchner funnel. Usually put 1cm of 20mesh and 1cm of 50mesh on top. If the filtration slows down. Stir the sand up a little. Also works well on other wackers with more demaning work-up.

Antibody has also wondered whether the ketal --> ketone is in fact spontaneous. If it weren’t that would certainly account for some mediocre aminations with O2 wacker ketone.Jimi loves ya

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Osmium

Yes, I worked up the post-Wacker reaction by adding a few drops of HCl and a little water and removing the bulk of the MeOH on the rotovap until a phase separation was visible (mixture became milky). Then more water was added and the ketone extracted with ether, followed by shaking the extract with conc. bisulfite solution.MeOH removal was done under vacuum, so the temp wasn't that high (~40°C). Flooding with water and a little bit HCl should work just the same, as far as I know these ketals are easily hydrolysed.But I agree, that is a very good point. The ketal is pretty stable in basic pH and will not aminate.

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KrZ

frost

isnt that kind of like the ts11 100g safrole150cc tol100cc h2o2 30%" " added at 6 hours" " 12 hours" " 18 hours2.5cc gaa1g pd (aco)260cdual phase reaction that takes 24 hours and yields 80%dosent h202 degrade over time so wouldent more be needed if time was increased?if temp is decreased reaction time is inmcreased, so wouldent adding more catylyst be a good idea even in the o2 if running colder 55f push it in the right direction and prevent side resctions like isosafrole?wouldent 500ml tert butyl alcohol be better than tol, and just omit the a.a. add all the h2o2 (400mls)over 30 mins to 200g safrole and 1g pd(aco)2 at 78-80c maintained over 6 hours ending up with a ph of 2 and ketone not ketal?seperate with equal vol of water then extract with dcm.this reaction is highly selective so no iso would be produced i'm assuming according to refs on it.frost

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psychokitty

KrZ, please refer me to the appropriate thread. I hope you didn't delete all of your posts.

Now, the only gripe that I have is with the inconsistency of your reports regarding this method. If the stainless steel interior of the "soda-keg" does indeed react with the PdCl2 and CuCl2 in solution (as it did on my FIRST and SECOND try to yield a high content of 2-alkene) how were you able to process the amounts of ketone (how much, I won't say) that you claimed you did (via e-mail and such) over a period of over 3-4 months?

All that time, before the advent of the new Hive, you were reporting high conversion factors, accidental hose ruptures -- the O2 heating up and the hose going BOOM!, remember? -- so when exactly did this stainless steel problem arise exactly?